Residential and commercial water systems, e.g., residential waste water treatment systems and evaporative cooling towers for air conditioning, are subject to contamination from the presence and growth of microbes, e.g., algae, pathogenic bacteria and fungi. The sanitization of such water systems including, but not limited to, recirculating water systems, often involves introducing a hypochlorite anion donor material, such as calcium hypochlorite, into the water system so as to establish a desired level, e.g., a sanitizing amount, of free available chlorine (FAC) within the water system. The presence of free available chlorine serves to eradicate or control deleterious amounts of undesirable microbial species that are found in the water comprising the water system, the existence of which microbial species can lead to the development of infection or disease in humans and animals.
Free available chlorine (FAC) can be established and maintained in such water systems by adding regularly a source of hypochlorous acid (HOCl) or hypochlorite anion (ClO−), e.g., calcium hypochlorite or an aqueous solution of calcium hypochlorite, to the water. FAC levels of from 1 to 45, e.g., from 1 to 10 parts per million parts of water (ppm), sometimes reported as milligrams per Liter (mg/L), are commonly maintained in recreational water systems. FAC levels of 1 ppm or less, e.g., 0.5 to 1 ppm, are commonly maintained in cooling water systems. Water having a FAC content in amounts of greater than 10 ppm (generally in the range of hundreds to thousands of mg/L) can be used to sanitize surfaces or articles to which it is applied, e.g., food, equipment and tables used for the processing of raw food or in the preparation of processed food products.
Hypochlorous acid or hypochlorite anion can be introduced into water by passing the water through an apparatus (often referred to as a feeder), e.g., a container having a canister that contains calcium hypochlorite material, which is usually in the form of granules, tablets or pellets. When water is introduced into such a container and into contact with the calcium hypochlorite within the canister, the calcium hypochlorite dissolves, thereby forming an aqueous solution comprising hypochlorite anion. This solution may be mixed with a water supply, added to water to be sanitized, or used directly for the intended application.
In some commercial applications, such as waste water or cooling tower applications, the container holding the calcium hypochlorite material may receive infrequent attention, e.g., monthly or for longer intervals. If the calcium hypochlorite material within the container is exposed to humid conditions for an extended length of time, the portion of the calcium hypochlorite not in direct contact with water can absorb water. In that circumstance, the solid calcium hypochlorite material, e.g., tablets of calcium hypochlorite, can become soft and swollen, and develop a consistency similar to mush. Such expanded calcium hypochlorite tablets may hang-up in the container, which can cause an upset in the amount and delivery rate of the aqueous solution comprising hypochlorous acid/hypochlorite anion. In some instances, the calcium hypochlorite within the container is consumed prematurely.
Minor amounts of discrete particulate Group IIA or IIIA (of the Periodic Chart of the Elements) metal stearates, e.g., calcium stearate or aluminum stearate, have been added to calcium hypochlorite to slow its dissolution in water and to minimize its absorption of water. However, such discrete Group IIA and IIIA metal stearates may cause problems in the production of metal stearate-calcium hypochlorite mixtures, particularly in the process of producing formed articles, e.g., tablets. For example, in the preparation of metal stearate-calcium hypochlorite mixtures, dust collectors are often used to collect airborne particles of calcium hypochlorite and metal stearate, thereby to maintain an environmentally safer and more pleasant working environment. The foregoing metal stearates, e.g., calcium stearate or aluminum stearate, are generally used in a finely-divided powdery form. Consequently, the metal stearate powder can become easily airborne, and is eventually collected in the dust collector and air ducts associated with the dust collector, where it can reach elevated concentrations, vis-à-vis, the concentration of the metal stearate in the calcium hypochlorite formed article. Because of the hot conditions and the elevated concentration of metal stearate in the calcium hypochlorite-metal stearate mixture that can exist in such dust collector equipment, the calcium hypochlorite in the dust collector equipment may become unstable. Consequently, it is desirable that the preparation of such mixtures be avoided.
It would, therefore, be advantageous to develop a solid calcium hypochlorite composition that has reduced hydrophilicity (affinity for water), vis-à-vis, commercial grades of unblended calcium hypochlorite, and the preparation of which solid composition does not have the aforedescribed production problems. It would also be desirable that such a solid calcium hypochlorite composition have a FAC content that is at least sufficient to allow its practical use for the batch and/or continuous sanitization of water systems, e.g., recirculating water systems such as evaporative cooling tower waters, evaporative condensers, residential waste water treatment systems, etc.